Fix issue with flickering with recents animation

The flicker is caused by executeAppTransition only being called
after the closing activity has finished pausing, probably because
it can enter PIP.

We don't need to wait for the activity to finish pausing in this
case - just execute the transaction and destroy the surfaces
already!

Test: go/wm-smoke
Test: Swipe up on PIPable activity with new Launcher APK
Change-Id: I92efef97b157a13e4670eb0c7e7113afa50302d5